Because of increasingly strict solvent emission regulations in recent years, low solvent emission paints have become very desirable. A number of high solids paint compositions have been proposed to meet these low solvent emission requirements. However, many of the compositions are deficient because of difficulty in application, slow curing rates, complex and/or time consuming composition formulation, poor durability and low solvent and water resistance of the coating.
One composition, which has been proposed to overcome these deficiencies is taught in U.S. application Ser. No. 334,684, filed Dec. 12, 1981, now U.S. Pat. No. 4,394,486, in the name of the inventors of this application. In that composition, hydroxy functional acrylic copolymers react with anhydrides of dicarboxylic acids to produce hydroxy acid and polyacid copolymers. The composition of such a mixture is largely dictated by the stoichiometry of the reactants employed. These acid products are then reacted with epoxies to produce hydroxy functional resins. Subsequently a composition comprising a mixture of these hydroxy functional resins and amine-aldehyde crosslinking agent can be applied to a substrate and cured at elevated temperatures to obtain a crosslinked structure. Unexpectedly, we have now found that all of the aforementioned reactions can be carried out in situ during curing on the substrate to obtain high solids coatings with excellent physical properties. While not wishing to be bound by theory, it is believed that in this reaction sequence the hydroxyl functionality of the glycidyl hydroxy acrylic copolymer reacts with the anhydride to produce acid functionality which further reacts with the epoxide functionality of the copolymer to produce hydroxyl moiety; then at higher temperatures, the amine-aldehyde reacts with the hydroxyl functionality to produce a crosslinked network. This crosslinking reaction is facilitated by the unconsumed acid present in the composition.